Not many people put “a basement for building a boat” in their plans for a new-build house. But then, at first, Tim and Jo Lucas didn’t even plan to build a house. In September 2009, having sold their Stoke Newington home, they were looking for a house in or around Kew, for them and their daughters, Rosalind, now seven and Alex, six.

When Tim registered online with a local estate agent and typed “under £500,000” in the search box, their plans took a new direction. Up came a site with seven garages on it — former stables. This set the couple thinking.

The result? An extraordinary, double-gabled, 4,000sq ft house, its steeply pitched, twin-peak roofs made of 4mm-thick Corten, a steel that rusts to a gorgeous velvety orange, springing from walls that once were part of a coach house. Between the two pitched sections is an amazing glass middle with a steel staircase running up inside, tall enough for a Christmas tree to vie with Trafalgar Square.

But that’s just the beginning. The roofs were made in pre-cut sections done by computer, swung up on cranes, and welded. Remarkably, no scaffolding was used to build this house. Some areas of steel are perforated, letting in dappled light to give a Moroccan feel — so in the master bedroom, which soars like a cathedral to the roof ridge, a daybed with a screened window makes the perfect place to read.

The house was designed around both parents and children. Rosalind designed her own bed, and a cupboard with lots of secret places.

The palette is simple throughout, while the floors are Danish Dinesen timber. Interior timberwork is oak veneer with some sliding pocket doors, and other doors that open, do a second job concealing shelves. Tim’s brother, Sam, a joiner, fitted it all from a joinery workshop in the basement.

“I hate a redundant door and I’m obsessive about storage,” says Jo. Each drawer has a cutout hand pull, rather than a knob, while the cupboards have nothing — you just pull in the right place. But Jo caused a near riot with the kitchen. “I said I wanted it to be the centre of the house,” she says, “and they took me literally.” In fact, it is the courtyard that is the true centre, with the kitchen-diner leading out to it through floor-to-ceiling glass.

Eye-catching: the family’s double-gabled house with weathered Corten steel roofs and glass central section
Many surprises follow, but none caps the wooden slide that runs from a square hole at the top of the stairs all the way to the basement, which has artificial turf. The girls gleefully demonstrate that it’s faster than the stairs. And here, in their current playroom, there is indeed the space to build a boat.

Tim, 40, and Jo, 39, met in Berlin in 2000, both structural engineers working for top company Arup. Jo, who is Australian, comes from a family of builders. Since both are in the construction field, they know lots of architects. Tim told his friend, architect Stuart Piercy, about the site, and Piercy suggested building a house on it, which Tim and Jo would project manage.

There were many constraints on the plot. It was in a tightly built, mainly Victorian conservation area, with a mixture of brick house styles. Piercy made an early, informal application to the planners for a modern house of rusting steel and glass. “He got a sort-of yes,” says Tim. So the couple bought the land for £400,000.

They put in a full application in October 2010 and were able to begin the following spring after a few changes, such as making the roof lower than the rest of the street. But where is the usual catalogue of problems? Tim and Jo knew what they wanted and how to make it, and worked with Piercy to create what they had visualised, so that the house almost designed itself.

Finance was a different matter. “My parents couldn’t believe the hoops we had to jump through,” says Jo. “In Australia, everything is set up for self-building, everyone self-builds. But here, there is only one mortgage, so the rate is too high. It was very difficult to borrow money, and we ran out halfway through and had to borrow more.”

She adds: “No one else could have built this house. It was a combination of Tim’s and my skills. People just had to believe in us — and Stuart Piercy is very confident, which also helped.”

The finished house is a combination of practical and magical. Jo is especially pleased with its effect on their children. “The world turned up in this house,” she says. “Women and men architects, joiners and workers from many nationalities. They all included the girls in what they were doing, so now they both feel confident that, in the future, they too can mould their own world. That’s the gift this house has given them.”